Nissan idle issue

[StrutnBPS]

1994 Nissan truck. Replaced engine with new one. Drove it 3 years (4,000) miles. All of a sudden idle went crazy to around 5,000 rpm. Replaced MAP, vacuum lines, and a few other things. Got better but still idles at 1,000-2,000 rpm. Once there’s a load on it, it runs fine. Any ideas?

[Gone South]

I’m not familiar with those trucks or whether you have a 4cyl or v6. I would try pinching each vacuum line shut to find if one is leaking or cracked or if brake booster diaphragm is bad. Check the idle air controller it could be stuck open from carbon buildup, not a bad idea to clean it out anyway. Less likely but still possible that you have a manifold gasket failing or manifold sealing surface loose. I’m not sure if you have an adjustable tps sensor on that motor but that can cause high revs on startup/idle too.

[StrutnBPS]

It’s a truck I am looking to possibly buy for my dad to use as a hunting truck. These are the things that have been done to it, but it still will not idle correctly. And it’s a 4cly

MAP replaced
O2 sensor
Air control Valve
Idle stop valve
Throttle sensor
All new injectors
Vacuum hoses

The owner has tried relearning/calibrating the sensors per manual.

I have a video of the engine running, but I don’t know how to post?